The present invention relates to the field of sensors and is more particularly directed to the area of calibration of sensors. This application is related to U.S. patent application Ser. No. 08/175,911 entitled "Embedded Programmable Sensor Apparatus by the same applicant and is commonly assigned with the present application.
Since the inception of electronic sensors, calibration of sensors have imposed a substantial cost on sensor cost to the end user of the sensor. Generally, three calibrations were required depending upon the end use of the sensor.
An initial calibration was usually performed by the sensor manufacturer to make sure that broad desired tolerances are met. This calibration process in current times involved laser tailoring of a bias resistor network to a desired resistance. This process typically would require multiple passes and total elapsed times in excess of 20 seconds when using median grade performance equipment.
Next, an original equipment manufacturer (OEM) would perform a calibration to ensure that the sensor met its needs. This was usually done by including at least one multi-turn potentiometer with the sensor and adjusting the potentiometer in a well known way until the desired performance characteristics were achieved. Finally, an epoxy could be placed on the potentiometer to freeze the setting. This was an expensive process.
Lastly, performance characteristics of sensors were affected by the conditions in which they were used in the field. Accordingly, field calibration was necessary to ensure that sensor performance was acceptable once the sensor was installed in its intended application. Usually, this calibration involved further adjustments to multi-turn potentiometers.
One particular sensor of interest here was a flow sensor. Flow sensors were often used in Heating, Ventilating and Air Conditioning applications for, as an example, measuring air flow through ducts. This information could be used to control the temperature of a controlled room. Typically, such sensors were located within a HVAC controller. The controller typically operated on instructions stored by a memory and executed by a clocked arithmetic logic unit (ALU). The controller itself could be located within the overhead space of the room. This could make manual adjustment of potentiometers difficult once the controller was installed.
Accordingly, it is an object of the present invention to substantially eliminate the need for factory laser trimming of resistors during the calibration of sensors. It is a further object of the present invention to substantially reduce the need for using potentiometers to calibrate the sensor. It is yet another object of the present invention to reduce the cost of calibrating the sensor. It is still another object of the present invention to reduce the manual labor required to calibrate the sensor.